P2-B: Hebbian Updater (DELIVERS: connection plasticity)

[github-actions]

Why: Strengthen useful connections, decay unused ones. Edge changes alter σ(v) values and can trigger hotpath promotions or evictions.

• P2-B1: Implement daydreamer/HebbianUpdater.ts

  • LTP: strengthen edges traversed during successful queries
  • LTD: decay all edges by small factor each pass
  • Prune: remove edges below threshold; keep Metroid degree within HotpathPolicy-derived bounds
  • After LTP/LTD: recompute σ(v) for all nodes whose incident edges changed (via SalienceEngine.batchComputeSalience)
  • Run promotion/eviction sweep for changed nodes via SalienceEngine.runPromotionSweep
  • Update MetadataStore.putEdges

• P2-B2: Add Hebbian test coverage

  • tests/daydreamer/HebbianUpdater.test.ts
  • Test strengthen increases weight
  • Test decay decreases weight
  • Test pruning removes weak edges and keeps degree within bounds
  • Test that salience is recomputed for changed nodes
  • Test that promotion sweep runs after LTP increases salience above weakest resident

Exit Criteria: Edge weights adapt based on usage; salience and hotpath updated accordingly.